The present invention relates to a caliper for measuring the thickness of each of a plurality of collated printed products, such as books, magazines, signatures, and the like, so as to determine whether the printed products contain the proper number of sheets.
In collating conveyor systems, it is common to incorporate a caliper along the path of travel of the products to check the thickness of each product and thereby verify that there has not been a malfunction in the collating process resulting in either missing sheets or excessive sheets. If a malfunction is detected, the caliper issues a signal which causes the non-complying product to be rejected or otherwise identified to permit the error to be corrected.
Calipers used with such systems in the past have typically comprised a lever arm which is moved into contact with the advancing products by means of an actuator, such as an air cylinder or a linear electric transducer, and a microswitch is provided which issues a go/no-go signal depending upon whether or not the lever arm has been pivoted by the actuator into the product to an elevation which indicates the proper number of sheets. Such prior devices require several mechanical linkages, and it is difficult to obtain highly accurate readings.
It is accordingly an object of the present invention to provide an improved caliper of the described type, which is highly accurate and reliable, and which is readily programmable to facilitate its initial set up and operation.